Holographic Colour Prints: Enhanced Optical Security by Combined Phase and Amplitude Control

TL;DR

This paper introduces a holographic colour print that combines phase and amplitude control at the pixel level to create a secure, multi-functional optical security device capable of displaying different holograms under various lighting conditions.

Contribution

It presents a novel fabrication method for integrated holographic colour prints with pixel-level phase and amplitude control, enabling advanced security features.

Findings

Multiple holograms can be projected with different laser illumination colors.

The print is fabricated using a single lithographic process.

Potential applications in document security.

Abstract

We created a novel optical security device that integrates multiple computer-generated holograms within a single colour image. Under white light, this "holographic colour print" appears as a colour image, whereas illumination with a red, green, or blue beam from a handheld laser pointer projects up to three different holograms onto a distant screen. In our design, all dielectric layered pixels comprising phase plates (phase control) and structural colour filters (amplitude control) are tiled to form a monolithic print, wherein pixel-level control over the phase and amplitude of light allows us to simultaneously achieve hologram multiplexing and colour image formation. The entire print is fabricated in a single lithographic process using a femtosecond 3D direct laser writer. As the phase and amplitude information is encoded in the surface relief of the structures, our prints can be manufactured using nanoimprint lithography and could find applications in document security.